/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.giraph.utils;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.util.ArrayList;

import org.apache.hadoop.conf.Configurable;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.util.ReflectionUtils;

/**
 * A Writable for ListArray containing instances of a class.
 *
 * @param <M> Message data
 */
public abstract class ArrayListWritable<M extends Writable> extends ArrayList<M>
  implements Writable, Configurable {
  /** Defining a layout version for a serializable class. */
  private static final long serialVersionUID = 1L;
  /** Used for instantiation */
  private Class<M> refClass = null;

  /** Configuration */
  private Configuration conf;

  /**
   * Using the default constructor requires that the user implement
   * setClass(), guaranteed to be invoked prior to instantiation in
   * readFields()
   */
  public ArrayListWritable() {
  }

  /**
   * Constructor with another {@link ArrayListWritable}.
   *
   * @param arrayListWritable Array list to be used internally.
   */
  public ArrayListWritable(ArrayListWritable<M> arrayListWritable) {
    super(arrayListWritable);
  }

  /**
   * This constructor allows setting the refClass during construction.
   *
   * @param refClass internal type class
   */
  public ArrayListWritable(Class<M> refClass) {
    super();
    this.refClass = refClass;
  }

  /**
   * This is a one-time operation to set the class type
   *
   * @param refClass internal type class
   */
  public void setClass(Class<M> refClass) {
    if (this.refClass != null) {
      throw new RuntimeException(
          "setClass: refClass is already set to " +
              this.refClass.getName());
    }
    this.refClass = refClass;
  }

  /**
   * Subclasses must set the class type appropriately and can use
   * setClass(Class<M> refClass) to do it.
   */
  public abstract void setClass();

  @Override
  public void readFields(DataInput in) throws IOException {
    if (this.refClass == null) {
      setClass();
    }
    int numValues = in.readInt();            // read number of values
    ensureCapacity(numValues);
    for (int i = 0; i < numValues; i++) {
      M value = ReflectionUtils.newInstance(refClass, conf);
      value.readFields(in);                // read a value
      add(value);                          // store it in values
    }
  }

  @Override
  public void write(DataOutput out) throws IOException {
    int numValues = size();
    out.writeInt(numValues);                 // write number of values
    for (int i = 0; i < numValues; i++) {
      get(i).write(out);
    }
  }

  @Override
  public final Configuration getConf() {
    return conf;
  }

  @Override
  public final void setConf(Configuration conf) {
    this.conf = conf;
  }
}
